A giant dust-busting astronomical telescope in Chile has zoomed in on the heart of our Milky Way galaxy and captured more than 84 million stars. An international team used Europe’s VISTA survey telescope to produce an incredibly detailed mosaic formed from thousands of separate images and made up of nearly nine billion pixels. 

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VISTA’s camera is especially sensitive to the warmth of infrared light which allowed it to record many stars that would normally be hidden behind vast clouds of dust and so invisible in optical light.

The image is so large (108,200 by 81,500 pixels) that if it were to be printed at the resolution of a typical book, it would be nine metres long and seven metres high. But it wasn’t just taken as a pretty picture, of course.

Cataloguing the many millions of stars in this one small central region of the Milky Way will help scientists understand more clearly what lies at the centre of our galaxy and how it developed.

Chile’s Roberto Saito, who led the study, said: “By observing in detail the myriads of stars surrounding the centre of the Milky Way we can learn a lot more about the formation and evolution of not only our galaxy, but also spiral galaxies in general.”

VISTA stands for the Visible and Infrared Survey Telescope for Astronomy and it stands at the European Southern Observatory’s Paranal site high in the Atacama Desert, not far from the domes of the Very Large Telescope (VLT). The writer visited last year and took the accompanying photo of VISTA, with its powerful light-gathering 4.1-metre mirror.

Our Milky Way resembles most other spiral galaxies in having a huge concentration of ancient stars at its centre in what astronomers term the bulge. But it is a region that is normally very hard to see. Data from one of the telescope’s surveys, the VISTA Variables in the Via Lactea programme (VVV), was used to produce the picture.

Co-author of the study Dante Minniti, also of Chile, said: “Observations of the bulge of the Milky Way are very hard because it is obscured by dust. To peer into the heart of the galaxy, we need to observe in infrared light, which is less affected by the dust.”

Information collected from this image, one of the biggest ever taken in astronomy, was used to compile the largest ever catalogue of the central mass of stars in the Milky Way. To analyse it, the brightness of each star was plotted against its colour to created a graphic diagram produced from ten times more stars than in any study before and covering the entire bulge. The results help astronomers to study the stars’ different properties, such as their temperature, age and size, or mass.

Minniti added: “Each star occupies a particular spot in this diagram at any moment during its lifetime. Where it falls depends on how bright it is and how hot it is. Since the new data gives us a snapshot of all the stars in one go, we can now make a census of all the stars in this part of the Milky Way.”

Astronomers will be mining the data for many years to come. But one surprise already from the survey was the number of faint red dwarf stars detected. These will be prime targets to examine in the search for transiting exoplanets.

VISTA was conceived, designed an built by UK astronomers and engineers, overseen by the UK Astronomy Technology Centre in Edinburgh. Jim Emerson from Queen Mary, University of London, which leads the VISTA consortium said: “This gigantic image is an impressive testament to the quality of the images being taken at the VISTA telescope.

“The unprecedented detail on numbers, types, and locations of stars towards the centre of our Galaxy is giving us exciting new tools to test competing models for how our galaxy is really structured and came to be as it is.”

Professor Richard Holdaway, Director of RAL Space in Oxfordshire where the camera was built, said; “Sometimes in astronomy there are moments when you simply think, wow! This is one of those times. The detail unveiled through the scale of the image and the technical excellence by the teams who helped achieve this is incredible. It really will allow us to push the boundaries of what we know about our home galaxy.”

Roberto Saito represents the Pontificia Universidad Católica de Chile, Universidad de Valparaíso and The Milky Way Millennium Nucleus, Chile. Dante Minniti is also from the Pontificia Universidad Catolica de Chile. You can go here to view the whole enormous picture. The results are reported in the journal Astronomy & Astrophysics.